Posted on by Fraser Cain

Planetary Systems Seen Forming

Two of NASA’s Great Observatories, the Spitzer Space Telescope and the Hubble Space Telescope, have provided astronomers an unprecedented look at dusty planetary debris around stars the size of our sun.

Spitzer has discovered for the first time dusty discs around mature, sun-like stars known to have planets. Hubble captured the most detailed image ever of a brighter disc circling a much younger sun-like star. The findings offer “snapshots” of the process by which our own solar system evolved, from its dusty and chaotic beginnings to its more settled present-day state.

“Young stars have huge reservoirs of planet-building materials, while older ones have only leftover piles of rubble. Hubble saw the reservoirs and Spitzer, the rubble,” said Dr. Charles Beichman of NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif. He is lead author of the Spitzer study. “This demonstrates how the two telescopes complement each other,” he added.

The young star observed by Hubble is 50 to 250 million years old. This is old enough to theoretically have gas planets, but young enough that rocky planets like Earth may still be forming. The six older stars studied by Spitzer average 4 billion years old, nearly the same age as the sun. They are known to have gas planets, and rocky planets may also be present. Prior to the findings, rings of planetary debris, or “debris discs,” around stars the size of the sun had rarely been observed, because they are fainter and more difficult to see than those around more massive stars.

“The new Hubble image gives us the best look so far at reflected light from a disc around a star the mass of the sun,” said Hubble study lead author, Dr. David Ardila of the Johns Hopkins University, Baltimore. “Basically, it shows one of the possible pasts of our own solar system,” he said.

Debris discs around older stars the same size and age as our sun, including those hosting known planets, are even harder to detect. These discs are 10 to 100 times thinner than the ones around young stars. Spitzer’s highly sensitive infrared detectors were able to sense their warm glow for the first time.

“Spitzer has established the first direct link between planets and discs,” Beichman said. “Now, we can study the relationship between the two.” These studies will help future planet-hunting missions, including NASA’s Terrestrial Planet Finder and the Space Interferometry Mission, predict which stars have planets. Finding and studying planets around other stars is a key goal of NASA’s exploration mission.

Rocky planets arise out of large clouds of dust that envelop young stars. Dust particles collide and stick together, until a planet eventually forms. Sometimes the accumulating bodies crash together and shatter. Debris from these collisions collects into giant doughnut-shaped discs, the centers of which may be carved out by orbiting planets. With time, the discs fade and a smaller, stable debris disc, like the comet-filled Kuiper Belt in our own solar system, is all that is left.

The debris disc imaged by Hubble surrounds the sun-like star called HD 107146, located 88 light-years away. John Krist, a JPL astronomer, also used Hubble to capture another disc around a smaller star, a red dwarf called AU Microscopii, located 32 light-years away and only 12 million years old. The Hubble view reveals a gap in the disc, where planets may have swept up dust and cleared a path. The disc around HD 107146 also has an inner gap.

Beichman and his colleagues at JPL and the University of Arizona, Tucson, used Spitzer to scan 26 older sun-like stars with known planets, and found six with Kuiper Belt-like debris discs. The stars range from 50 to 160 light-years away. Their discs are about 100 times fainter than those recently imaged by Hubble, and about 100 times brighter than the debris disc around the sun. These discs are also punctuated by holes at their centers.

Both Hubble images were taken with the advanced camera for surveys. They will be published in the Astronomical Journal and the Astrophysical Journal Letters. The Spitzer observations are from the multiband imaging photometer and will appear in the Astrophysical Journal.

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

Original Source: Hubble News Release

Posted on by Fraser Cain

Tarantula Nebula in Detail

The Tarantula Nebula is one of the most impressive views in the Southern sky, cf. ESO Press Photos 14a-g/02. Visible to the unaided eye in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way that is located in the direction of the southern constellation Doradus at a distance of about 170,000 light-years, this huge nebula is the prototype of what astronomers refer to as a “Giant HII region”. In this complex of glowing gas and very hot and luminous stars, the gas is mainly composed of protons and electrons, which are kept apart by energetic photons emitted by the stars in this area.

The Tarantula Nebula (also designated 30 Doradus) owes its name to the arrangement of its brightest patches of nebulosity that somewhat resemble the legs of a spider. They extend from a central “body” where a cluster of hot stars (designated “R136”) resides that illuminate the nebula. This name, of the biggest spiders on the Earth, is also very fitting in view of the gigantic proportions of the celestial nebula – it measures nearly 1,000 light years across!

While the central regions of 30 Doradus may be compared to a tarantula, the entangled filaments in the outskirts of this nebula – some of which are seen in PR Photo 34a/04 – could well be likened with its cobweb. They testify to an ongoing history of very vigorous activity and make this spectacular sky region a showcase of dramatic effects caused by the tremendous output of energy from the most massive stars known.

Intricate colours
The marvellous richness of the filament colours is due to the varying conditions in the interstellar gas in this region, cf. PR Photo 34b/04. The red in these images is caused by emission of excited hydrogen atoms, the green shades correspond to emission from oxygen atoms from which two electrons (“doubly-ionized oxygen”) have been “knocked off” by the energetic radiation of hot stars in the R136 cluster, that is located beyond the lower right corner of this photo. The intensity of this emission increases towards R136, explaining the yellowish colour near the edge of the photo.

A blue colour is contributed by singly-ionized atoms of oxygen. Other atoms like nitrogen and sulfur at different levels of ionization also add to the emission of the nebula at specific wavelengths. The observed colours thus probe the physical condition of the emitting gas and the temperature of the star(s) that excite(s) it. The intricate appearance of the filaments is mostly a consequence of turbulence in the interstellar gas, of the magnetic fields, and of the energy input by the massive stars in the neighbourhood.
Supernovae blow interstellar “bubbles”

The large ring-shaped nebula slightly to the lower-left (South-East) of the centre of PR 34a/04 is known as DEM L 299 [1]. Detailed investigations show that it represents an “interstellar bubble” which was “blown” by supernovae explosions, most probably happening millions of years ago, as massive stars near the centre of this structure ended their comparatively short lives in glorious flashes.

A closer inspection shows that another supernova exploded somewhat later near the rim, forming a bright and more compact nebula known as SNR 0543-689 (PR 34c/04). Other supernovae in this general field exploded even more recently, such as the one that created the remnant B0544-6910 (PR 34d/04) only a few tens of thousands of years ago, a blink of an eye by all astronomical standards.

Nebulae with built-in powerhouses
Not all the nebulae seen in this region are caused by supernovae, however. The glow of N 164 [1], a bright, extended red-yellow nebula just below DEM L 299, is mostly due to its own “private” powerhouse, that consists of several massive stars deeply embedded in its interior (PR Photo 34e/04).

The same holds for DEM L 297, the somewhat smaller and fainter nebula to the right of DEM L 299 (PR Photo 34f/04). It is divided into two half-circle formed segments by a dark lane of interstellar dust in front of it. Indeed, within the Tarantula complex many such dark and dusty clouds are seen in silhouette as they obscure bright nebulosity behind them.

Many stellar clusters
The outskirts of the Tarantula Nebula are also rich in stellar clusters. One of them, NGC 2093 [1], cf. PR Photo 34g/04, has relatively few stars and is relatively young, just a few tens of millions of years. It appears that its stars have already excavated a sizeable cavity around them that is now relatively void of gas.

An older and much more compact cluster, NGC 2108, is seen near the bottom of PR Photo 34h/04 and reproduced in full in PR Photo 34a/04. It resembles the globular clusters in our own Galaxy, but it formed much more recently, about 600 million years ago. Still, NGC 2108 is much older than the Tarantula complex and it is quite possible that in its “youth” it was the core of another giant HII region that has since dissolved into interstellar space.

The images for this release were produced by two ESO astronomers who are impressed by this sky region. Nausicaa Delmotte did the observations for her thesis and notes that: “many of the nebulae and clusters seen in these photos would stand out prominently if they were located elsewhere in the sky and not this close to the core of the spectacular Tarantula complex.”. She is echoed by her colleague, Fernando Comeron: “This amazing concentration of clusters, HII regions, supernova remnants, and extremely hot and luminous stars in a single region makes the Tarantula in the LMC a unique celestial object, unrivalled in our own Galaxy and other nearby galaxies!”.
Note

[1]: The designation “DEM L 299” indicates that this object is no. 299 in the list of nebulae in the Large and Small Magellanic Clouds published in 1976 by astronomers R.D.Davies, K.H.Elliott and J.Meaburn. “N” refers to a list of bright nebulae in these galaxies that was compiled in 1956 by K.G.Henize. “NGC” stands for the “New General Catalogue” published in 1888 by J.L.E. Dreyer.

Original Source: ESO News Release

Posted on by Fraser Cain

Streaks Across Dione

A gorgeous Dione poses for Cassini, with shadowed craters and bright, wispy streaks first observed by the Voyager spacecraft 24 years ago. The wispy areas will be imaged at higher resolution in mid-December 2004. Subtle variations in brightness across the surface of this moon are visible here as well. Dione’s diameter is 1,118 kilometers, (695 miles).

The image shows primarily the trailing hemisphere of Dione, which is the side opposite the moon’s direction of motion in its orbit. The image has been rotated so that north is up.

The image was taken in visible light with the Cassini spacecraft narrow angle camera on Oct. 27, 2004, at a distance of about 1.2 million kilometers (746,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 28 degrees. The image scale is 3.5 kilometers (2.2 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

People, Not Robots, Should Upgrade Hubble

To ensure continuation of the extraordinary scientific output of the Hubble Space Telescope and to prepare for its eventual de-orbiting, NASA should send a space shuttle mission, not a robotic one, says a new congressionally requested report from the National Academies’ National Research Council. The agency should consider launching the manned mission as early as possible after the space shuttle is deemed safe to fly again, because some of the telescope’s components could degrade to the point where it would no longer be usable or could not be safely de-orbited, said the committee that wrote the report.

“A shuttle servicing mission is the best option for extending the life of the Hubble telescope and ultimately de-orbiting it safely,” said committee chair Louis J. Lanzerotti, distinguished research professor at the New Jersey Institute of Technology, Newark, and consultant, Bell Laboratories, Lucent Technologies, Murray Hill, N.J. “NASA’s current planned robotic mission is significantly more technologically risky, so a robotic mission should be pursued only for the eventual removal of the Hubble telescope from orbit, not for an attempt to upgrade it. Also, a shuttle mission could be used to place equipment on the telescope to make a robotic de-orbiting mission more feasible.”

The Hubble telescope, which has operated continuously in orbit for the past 14 years, was designed to be serviced regularly by astronauts. Four servicing missions replaced nearly all the key components while increasing the telescope’s capabilities. The fifth and final mission — to replace aging batteries, fine-guidance sensors, gyroscopes, and two scientific instruments — was originally intended to be completed by a shuttle crew as well, but NASA is currently planning an unmanned mission to service the telescope robotically.

The committee’s principal concerns about a robotic mission are the risk of failing to develop it in time and the risk of a mission failure, as well as the possibility that the robot could critically damage the telescope. A robotic mission would face significant challenges in using its grapple system to perform autonomous close-proximity maneuvers and the final capture of the space telescope — activities that have no precedent in the history of the space program and whose chances of success are low, according to the committee.

“Our detailed analyses showed that the proposed robotic mission involves a level of complexity that is inconsistent with the current 39-month development schedule,” said Lanzerotti. “The design of such a mission, as well as the immaturity of the technology involved and the inability to respond to unforeseen failures, make it highly unlikely that NASA will be able to extend the scientific lifetime of the telescope through robotic servicing.”

The committee assessed the safety risks of a shuttle servicing mission by comparing shuttle missions to the International Space Station — to which NASA plans to send 25 to 30 more shuttle flights — and shuttle missions to the Hubble telescope. The differences between the risks faced by the crew of a single shuttle mission to the space station and the risks faced by the crew of a mission to the Hubble telescope are very small, the committee concluded.

Also, a shuttle crew would be able to successfully carry out unforeseen repairs to the Hubble telescope and develop innovative procedures for unexpected challenges in orbit, the report notes. Such contingencies have been successfully addressed on three of the four prior missions to the telescope. A robotic mission, on the other hand, might not be able to repair failures that it is not designed to address, possibly stalling the mission in its early stages.

“With the replacement of aging components and the installation of new science instruments, Hubble is expected to generate as many new discoveries about stars, extra-solar planets, and the far reaches of the universe as it has already produced so far, with images 10 times more sensitive than ever before,” Lanzerotti said.

Original Source: National Academies of Science

Posted on by Fraser Cain

Private Spaceflight Bill Passes

The U.S. Senate gave final congressional approval to the Commercial Space Launch Amendments Act (H.R. 5382) on Wednesday, which will allow private citizens to fly on suborbital launch vehicles at their own risk. Backers of this legislation said that it was necessary to encourage space tourism companies, like Richard Branson’s Virgin Galactic, to risk making flights in the United States. Those opposed to the bill were concerned that regulators would have to stand by until someone actually got hurt before changing the rules.

Posted on by Fraser Cain

Mission to Neptune Under Study

In 30 years, a nuclear-powered space exploration mission to Neptune and its moons may begin to reveal some of our solar system’s most elusive secrets about the formation of its planets — and recently discovered ones that developed around other stars.

This vision of the future is the focus of a 12-month planning study conducted by a diverse team of experts led by Boeing Satellite Systems and funded by NASA. It is one of 15 “Vision Mission” studies intended to develop concepts in the United States’ long-term space exploration plans. Neptune team member and radio scientist Professor Paul Steffes of the Georgia Institute of Technology’s School of Electrical and Computer Engineering calls the mission “the ultimate in deep space exploration.”

NASA has flown extensive missions to Jupiter and Saturn, referred to as the “gas giants” because they are predominantly made up of hydrogen and helium. By 2012, these investigations will have yielded significant information on the chemical and physical properties of these planets. Less is known about Neptune and Uranus — the “ice giants.”

“Because they are farther out, Neptune and Uranus represent something that contains more of the original – to use a ‘Carl Saganism’ – ‘solar stuff’ or the nebula that condensed to form planets,” Steffes said. “Neptune is a rawer planet. It is less influenced by near-sun materials, and it’s had fewer collisions with comets and asteroids. It’s more representative of the primordial solar system than Jupiter or Saturn.”

Also, because Neptune is so cold, its structure is different from Jupiter and Saturn. A mission to investigate the origin and structure of Neptune — expected to launch between 2016 and 2018 and arrive around 2035 — will increase scientists’ understanding of diverse planetary formation in our solar system and in others, Steffes noted.

The mission team is also interested in exploring Neptune’s moons, especially Triton, which planetary scientists believe to be a Kuiper belt object. Such balls of ice are micro planets that can be up to 1,000 kilometers in diameter and are generally found in the outermost regions of our solar system. Based on studies to date, scientists believe Triton was not formed from Neptune materials, like most moons orbiting planets in our solar system. Instead, Triton is likely a Kuiper belt object that was accidentally pulled into Neptune’s orbit.

“Triton was formed way out in space,” Steffes said. “It is not even a close relative of Neptune. It’s an adopted child?. We believe Kuiper belt objects like Triton were key to the development of our solar system, so there’s a lot of interest in visiting Triton.”

Though they face a number of technical challenges — including entry probe design, and telecommunications and scientific instrument development — the Neptune Vision Mission team has developed an initial plan. Team members, including Steffes, have been presenting it this fall at a variety of scientific meetings to encourage feedback from other experts. On Dec. 17, they will present it again at the annual meeting of the American Geophysical Union. Their final recommendations are due to NASA in July 2005.

The plan is based on the availability of nuclear-electric propulsion technology under development in NASA’s Project Prometheus. A traditional chemical rocket would launch the spacecraft out of Earth orbit. Then an electric propulsion system powered by a small nuclear fission reactor – a modified submarine-type technology — would propel the spacecraft to its deep-space target. The propulsion system would generate thrust by expelling electrically charged particles called ions from its engines.

Because of the large scientific payload a nuclear-electric propelled spacecraft can carry and power, the Neptune mission holds great promise for scientific discovery, Steffes said.

The mission will employ electrical and optical sensors aboard the orbiter and three probes for sensing the nature of Neptune’s atmosphere, said Steffes, an expert in remote radio sensing of planetary atmospheres. Specifically, the mission will gather data on Neptune’s atmospheric elemental ratios relative to hydrogen and key isotopic ratios, as well as the planet’s gravity and magnetic fields. It will investigate global atmospheric circulation dynamics, meteorology and chemistry. On Triton, two landers will gather atmospheric and geochemical information near geysers on the surface.

The mission’s three entry probes will be dropped into Neptune’s atmosphere at three different latitudes – the equatorial zone, a mid-latitude and a polar region. Mission designers face the challenge of transmitting data from the probes through Neptune’s radiowave-absorbing atmosphere. Steffes’ lab at Georgia Tech has conducted extensive research and gained a thorough understanding of how to address this problem, he noted.

The mission team is still discussing how deep the probes should be deployed into Neptune’s atmosphere to get meaningful scientific data. “If we pick a low enough frequency of radio signals, we can go down to 500 to 1,000 Earth atmospheres, which is 7,500 pounds of pressure per square inch (PSI),” Steffes explained. “That pressure is similar to what a submarine experiences in the deep ocean.”

However, that depth will probably not be required, according to the mission team’s atmospheric modelers, Steffes said. The probes will be able to obtain most information at only 100 Earth atmospheres, or 1,500 PSI.

Original Source: Georgia Tech News Release

Posted on by Fraser Cain

Saturn’s C Ring

This view of Saturn’s outer C ring shows the extreme variations in brightness, along with the subtle, large-scale wavy variations discovered 24 years ago by NASA’s Voyager spacecraft. The notably dark Maxwell gap (near upper right) contains the bright, narrow and eccentric Maxwell ringlet, a Saturnian analog of the narrow Uranian epsilon ring. The gap also contains another very faint ringlet newly discovered by Cassini.

The image was taken with the Cassini spacecraft narrow angle camera on Oct. 29, 2004, at a distance of 838,000 (521,000 miles) from Saturn. The center of this view shows an area located approximately 81,300 kilometers (50,500 miles) from the planet. The image scale is 4.6 kilometers (2.9 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

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Study Negative on Hubble Repair

There has been tremendous controversy ever since NASA announced that they wouldn’t sending astronauts to repair and upgrade the aging Hubble Space Telescope. An independent report delivered to the agency says that even sending a robotic mission to repair the observatory is probably a bad idea – it would be too costly and risky. A robotic mission might take $2 billion or more to develop, might not reach Hubble in time, and probably only has a 50% chance of succeeding – it would be more cost effective to launch a new observatory with the instruments built for Hubble.

Posted on by Fraser Cain

Channels at Reull Vallis

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express spacecraft, shows a region of Reull Vallis in the southern hemisphere of Mars.

The image shows an area located at about latitude 42? South and longitude 102? East. The image was taken with a ground resolution of about 21 metres per pixel during Mars Express orbit 451 in May 2004.

Reull Vallis is an outflow channel that extends 1500 kilometres across Promethei Terra in the direction of Hellas Basin. It is approximately 20 kilometres wide and has cut into the surrounding plain to a depth of 1800 metres. It is the major outflow channel in the region and exhibits a high degree of surface modification, suggesting a complex evolution.

In this image, Reull Vallis extends from the east to the north-west and is connected to a tributary in the south (Teviot Vallis). Distinct parallel structures are visible in the channels, possibly caused by glacial flow of loose debris mixed with ice. Small depressions, located on the flow features, are probably caused by the sublimation of ice.

Numerous impact craters, visible on the flanks of the valley, have been filled with material from these flows. Distinct flow features can be recognised within impact craters, for example, the 15-kilometre wide crater in the west (bottom) of the image.

There is a clear morphological distinction between the heavily eroded south-west and the plains of the north-east, which have experienced much less erosion. While most landforms throughout the image have a rounded, softened appearance, younger structures have a distinctly sharp and raised morphology.

On the southern and western edges of the colour image, large impact craters are visible. Their diameters range from 15 to 35 kilometres. These craters have heavily eroded rims and are partly filled with material. Erosion has left distinct, branched gully systems at the edge of the large crater that is located on the southern edge of the image.

Original Source: ESA News Release

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Views of Iapetus

These spectacular Cassini images of Saturn?s moon Iapetus show an enticing world of contrasts.

These are the sharpest views of Iapetus from Cassini so far, and they represent better resolution than the best images of this moon achieved by NASA’s Voyager spacecraft. Images obtained using ultraviolet (centered at 338 nanometers), green (568 nanometers) and infrared (930 nanometers) filters were combined to produce the enhanced color views at left and center; the image at the right was obtained in visible white light. The images on the bottom row are identical to those on top, with the addition of an overlying coordinate grid.

These views show parts of the moon?s anti-Saturn side ? the side that faces away from the ringed planet–which will not be imaged again by Cassini until Sept., 2007. In the central view, part of the moon?s eastern edge was not imaged and appears to be cut off.

With a diameter of 1,436 kilometers (892 miles), Iapetus is Saturn’s third largest moon. It is famous for the dramatic contrasts in brightness on its surface ? the leading hemisphere is as dark as a freshly-tarred street, and the trailing hemisphere and poles almost as bright as snow.

Many impact craters can be seen in the bright terrain and in the transition zone between bright and dark, and for the first time in parts of the dark terrain. Also visible is a line of mountains that appear as a string of bright dots in the two color images at left, and on the eastern limb in the image at right. These mountains were originally detected in Voyager images, and might compete in height with the tallest mountains on Earth, Jupiter’s moon Io and possibly even Mars. Further observations will be required to precisely determine their heights. Interestingly, the line of peaks is aligned remarkably close to the equator of Iapetus.

The large circular feature rotating into view in the southern hemisphere is probably an impact structure with a diameter of more than 400 kilometers (250 miles), and was first seen in low-resolution Cassini images just two months earlier.

These images were taken with the Cassini spacecraft narrow angle camera between Oct, 15 and 20, 2004, at distances of 1.2, 1.1 and 1.3 million kilometers (746,000, 684,000 and 808,000 miles) from Iapetus, respectively. The Sun-Iapetus-spacecraft, or phase, angle changes from 88 to 144 degrees across the three images. The image scale is approximately 7 kilometers (4.5 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release